Benefits of Physical Machine Guards versus Light Curtains
When deciding on which type of machine guarding method is best for your specific needs, the choices typically fall into two categories: physical machine guards and light curtains.
Light curtains, or other presence-sensing devices, have long been a common method of industrial guarding ranging from automotive facilities to machine shops and fabrication plants. Sometimes, however, the associated risk and exposure of using some equipment leaves light curtains as an unacceptable choice, and this is where physical machine guards can be the solution that will most effectively eliminate risk and increase safety compliance.
The goal of light curtains is to provide safety by ceasing machine operations if an object crosses a specified safety zone. While these can be useful in for many applications, their biggest limitation is protection from secondary, physical, hazards. These can include flying debris, sparks, splash, smoke or flash commonly associated with robotic welding.
These secondary hazards are of particular importance when discussing point-of-operation guarding, when an operator needs to interact with the machine process. Now, there are some presence-sensing devices that can be utilized for point-of-operation guarding, but even with these there can be risks associated as seen in the following case study from OSHA.
Case History #5 An operator was bending metal parts using a 36- ton part-revolution power press brake that was foot-activated and equipped with a light curtain. About 3-4 inches of the light curtain had been “blanked out” during a previous part run. While adjusting a part at the point of operation, the employee accidentally activated the foot pedal and amputated three fingertips. Source: https://www.osha.gov/Publications/osha3170.pdf
Physical Machine Guards
With physical machine guards, many of the risks associated with using a light curtain in point-of operation guarding can be eliminated, especially when concerning secondary hazards when an operator is needed to interact with the machine, robot or process. For instance, machine protection doors like The Defender or automated or retractable welding curtains and screens, like the RollShield, allow for a higher level of safety and increased productivity through:
● Containment of secondary hazards
● An electronic and physical means of controlling access
● Reducing footprint of manufacturing cell by locating closer to the hazard, reducing the need for a “safety zone”
● Increasing productivity by locating closer to hazard and provides clear visual cue for operator to be on task
● Allows operator to pivot to load and unload parts due to reduced "safety zone" space requirements
While not as involved as point-of-operation from as risk assessment view, industrial machine guarding by use of perimeter safety fencing, like the RoboGuard, also has its advantages over light curtains, again when concerning secondary hazards. Utilizing safety fencing will limit and/or restrict access and exposure to conform with the required safety standards.
Ultimately each machine guarding application has its own set of risks, and you need to make your machine guarding decisions on a case-by-case basis based on the layout of the process and potential hazards associated with exposure to the machine guarding devices. But when it comes to machine guarding where secondary hazards are common, physical barriers will have the advantage over light curtains in their reduction of the risk and exposure to operators while stream-lining the operation, saving space and time.
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